1. Field of the Invention
This invention relates to a process for the conversion of azacycloalkane-2,2-diphosphonic acids into their alkali metal or ammonium salts, the salts being obtained in the form of freeflowing low-dust powders.
2. Statement of Related Art
In known processes for the neutralization of organophosphonic acids, the acids are combined in the form of aqueous solutions with aqueous solutions of alkali metal hydroxides or ammonia. The dilute aqueous solutions of the salts obtained in this way are unsuitable for use in this form, for example, in anhydrous or substantially anhydrous formulation. The trasport of dilute aqueous solutions also involves considerable costs. Accordingly, the water present in the dilute aqueous solutions has to be removed, and this is very expensive in terms of energy requirements, e.g. utilizing spray drying or drying on rollers. Apart from their high energy demand, these drying processes have other disadvantages. In spray drying, very fine powders are formed, quantities of which become entrained due to the strong movement of air; and this can lead to serious losses. Where solutions are concentrated by evaporation or roller dryers, for example, coarse agglomerates are generally formed and have to be subsequently ground.
U.S. Pat. No. 3,941,772 and 3,988,443 disclose such acids and their salts, and their use as sequestering agents, e.g. in the treatment of certain disease states.